Generally, an ink jet printing apparatus forms color images by stamping three primary color inks (C (cyan), M (magenta), and Y (yellow)) corresponding to three primary colors or four primary color inks (including K (black) in addition to the C, M, and Y) onto a printing object, and expresses additive colors by changes in dot density.
However, in expression of additive colors by changes in dot density, a subtle color cannot be satisfactorily expressed or a resultant image provides a sense of roughness.
As an inkjet printing apparatus solving this problem, for example, one is disclosed in Patent Document 1: Japanese Published Unexamined Patent Application No. H08-207318 as described below.
FIG. 7 is a schematic sectional view showing the ink jet printing apparatus described in the same publication. This ink jet printing apparatus 100 applies a voltage between a ring-shaped electrode 101 and an electrode plate 102 by a power supply 108, discharges a concentrated ink 104 from a liquid feed pipe 103, and forms a droplet made of the ink on a printing object 105 on the electrode plate 102. When adjusting the ink density, the concentrated ink 104 is sucked out of the liquid feed pipe 103, and simultaneously, a transparent solvent 107 is sucked out of the liquid feed pipe 106 and the concentrated ink is diluted by the transparent solvent, and the diluted droplet is discharged to form a droplet the ink density of which has been adjusted on the printing object 105.
[Patent Document 1]
Japanese Published Unexamined Patent Application No. H08-207318